I am about to buy the two component expansions, but I have heard reports that they are only really used in the two added scenarios (and in the main game very scarcely).

Does anyone have experience with this? Do the monsters and tiles add a signifixant amount of replayability to the main scenarios?

Worth noting is that it also adds 16 new investigators .

And 2 new stories.

Yeah, that's true. I am mostly doing it for the tiles/monsters though.

So, do they add significant replayability to the other scenarios?

Cycle has two maps playable only if you have access to these tiles; possibly there's an alternate map also for Shattered Bonds, but it's a life since I played that one (14 months or so), so, I'm not 100% sure. Clearly, more stuff coming in the future is very likely to have some alternate maps based on the tile collections